1. Field of the Invention
This invention relates to a method for extracting a metallic composition. More particularly, this invention relates to a method for extracting a metal selected from a group consisting of copper and iron. In one embodiment, the method uses chemical reaction to remove copper or iron to be regenerated and recycled.
2. Background of the Invention
The use of metallic copper and iron is wide spread in many industries. The uses of metallic copper extend from circuit boards to use as a stop off material in the metal finishing industry. The uses of iron are too numerous to mention.
Many of the industrial uses for copper involve copper leaching or removal at some stage of industrial processing. A number of problems are presently associated with removing metallic copper or iron including the problem of waste products associated with the removal of the metallic composition. These problems are even more pronounced when removing copper or iron from a non-same metal substrate thereby producing multiple waste products.
Several methods are available for the dissolution of copper or iron (M) from a substrate. One such method involves the use of hydrogen peroxide and an acid. The reaction generally proceeds via the reaction: EQU H.sub.2 O.sub.2 +HA+M.sub.(s).fwdarw.2H.sub.2 O+MA
Continued use of this reaction produces a solution that is saturated with MA salt. The saturated solution can then be treated by crystallizing out the MA salt in a hydrated form. CuA crystallization requires a large capital investment in a crystallizer, a first drawback to this method of copper or iron removal. Further, the large volume of water generated via the oxidation of copper or iron in the presence of H.sub.2 O.sub.2 and HA poses a problem. Copper or iron act as a catalyst in the decomposition of H.sub.2 O.sub.2, consuming up to 10 times the anticipated stoichiometric amount of hydrogen peroxide. Thus, even though approximately five molecules of water are removed with every molecule of MA salt precipitated in the crystallizer, water is still formed at a much greater rate than it is removed. Further still, the hydrogen peroxide/acid method of removing copper from a substrate is unappealing in that the consumed hydrogen peroxide and acid reactants must always be replaced at great expense, and the crystallized copper or iron salt is costly for disposal.
Another common method for removing copper or iron from a substrate utilizes ferric chloride. Ferric is reduced to ferrous, while the metallic copper or iron is oxidized to cupric or ferrous, respectively. This method also has its disadvantages. For copper, the ferrous/ferric/cupric end product mixture is usually acidic, and is considered hazardous waste and is very costly for disposal. The waste can be chemically treated by processing of the waste via cupric removal and acid neutralization. Federal and state regulations permitting, the treated and filtered neutralized iron solution can be discharged in plant effluent. The use of ferric chloride in dissolving copper or iron from a substrate is even more costly than the acid-peroxide method due to the extensive chemical processing requirements, and the complete consumption of the ferric chloride oxidizing agent.
Still another chemical process for dissolving copper or iron involves making the copper-containing substrate an anode in a plating cell. The main problem with this method is that the cell voltage must be kept below the oxidation potential of the underlying substrate to prevent substrate dissolution. Such low voltages require a very large substrate surface area for reasonable copper or iron oxidation reaction rates, frequently making the use of this method impractical.
Others have tried to overcome the above mentioned shortcomings (voluminous end products, hazardous end products, complete consumption of chemical reactants, large surface areas associated with electrolytic cells . . . ), but have met only limited success.
U.S. Pat. No. 3,669,651 to Spedden et al. discloses the ferric sulfate-sulfuric acid leaching of naturally occurring, copper-bearing materials, such as copper minerals in mine waste dumps, and recovery of the dissolved copper by precipitation on metallic iron. The leaching is carried out on a cyclic basis, with reduction of ferric ions prior to the copper precipitation step. The pregnant leach solution is treated with a controlled quantity of a water soluble reductant, such as sulfur dioxide or ammonium bisulfite, for a sufficient period of time in the presence of activated carbon to minimize the ferric ion content thereof while substantially completely consuming the active ions of the reductant so wasteful consumption of the iron precipitant will be prevented while insuring most effective precipitation of copper, and so as also to provide nourishment, when ammonium bisulfite is employed as a reductant, or iron-oxidizing bacteria normally present in the leach solution.
U.S. Pat. No. 5,372,684 teaches the leaching of copper scrap, reduced to particulate form having particle sizes not larger than 50 mm, in a suitable apparatus with a solution of ferric fluoroborate in fluoroboric acid. During leaching, copper is dissolved, with ferric fluoroborate simultaneously being reduced to ferrous fluoroborate according to the following reaction: EQU 2Fe(BF.sub.4).sub.3 +Cu.fwdarw.Cu(BF.sub.4).sub.2 +2Fe(BF.sub.4).sub.2 (1)
The resulting solution is fed to the cathodic compartment of a diaphragm cell, in which copper is deposited, in compact and highly pure form, on a stainless steel cathode, from which it is periodically recovered. Neither of these inventions overcome all of the problems presently encountered when removing copper from a substrate.
U.S. Pat. No. 3,669,651, applying to a mine waste dump setting, requires either bacterial oxidation of Fe.sup.+2 ions to Fe.sup.+3 ions or the costly consumption of an additional oxidizing agent to regenerate ferric. Further, the ammonium bisulfite must regularly be replenished at an expense.
U.S. Pat. No. 5,372,684 requires the handling of the corrosive and costly flouroboric acid. Further, the reaction conditions require a low pH of less than 1 or the reaction conditions to be practicable in an industrial setting, or else the copper scrap mu t be manually ground down to a particle size of less than 50 mm.
It is therefore an object of the present invention to provide a chemical process for selectively removing a metallic substance, more particularly copper or iron wherein the process is inexpensive and utilizes relatively, safe chemical components.
It is further an object of the present invention to provide a chemical process for selectively removing copper or iron wherein the copper or iron is ultimately converted to a non-hazardous form that can be easily handled and inexpensively discarded.
It is further an object of the present invention to provide a chemical process for selectively removing copper or iron through a chemical reaction wherein the copper or iron can selectively be plated out in an electrolytic cell so that the copper or iron waste product can be easily handled and inexpensively disposed of.
It is further an object of the present invention to provide a chemical process for selectively removing copper or iron wherein an oxidizing agents is utilized to remove the copper or iron and wherein the reduced oxidizing agent is recyclable, thereby avoiding the need to constantly replenish costly oxidizing agents.
It is further an object of the present invention to provide a chemical process for selectively removing copper or iron wherein an oxidizing agent is utilize to remove the copper or iron, wherein the reduced oxidizing agent is recyclable and wherein electricity is used to both regenerate the expended oxidizing agent and to treat the chemically removed copper or iron waste in an inexpensive and cost effective manner.
It is further an object of the present invention to provide an improved chemical process for leaching copper or iron which may be operated continuously.
It is further an object of the present invention to provide an improved chemical process for leaching copper or iron from a substrate which may be operated continuously and wherein the leaching reaction may be controlled by monitoring the chemical components of an acid bath and/or the anode and cathode chambers of an electrolytic cell.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention and the detailed description setting forth the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.